Reciprocity of thermal diffusion in time-modulated systems

The reciprocity principle governs the symmetry in transmission of electromagnetic and acoustic waves, as well as the diffusion of heat between two points in space, with important consequences for thermal management and energy harvesting. There has been significant recent interest in materials with time-modulated properties, which have been shown to efficiently break reciprocity for light, sound, and even charge diffusion. However, time modulation may not be a plausible approach to break thermal reciprocity, in contrast to the usual perception. We establish a theoretical framework to accurately describe the behavior of diffusive processes under time modulation, and prove that thermal reciprocity in dynamic materials is generally preserved by the continuity equation, unless some external bias or special material is considered. We then experimentally demonstrate reciprocal heat transfer in a time-modulated device. Our findings correct previous misconceptions regarding reciprocity breaking for thermal diffusion, revealing the generality of symmetry constraints in heat transfer, and clarifying its differences from other transport processes in what concerns the principles of reciprocity and microscopic reversibility.

PELATIHAN DAN PENDAMPINGAN PEMBELAJARAN DARING BERBASIS MOODLE UNTUK GURU FISIKA SMA DI KABUPATEN MALANG SELAMA MASA PANDEMI COVID-19

ABSTRAKDampak dari pendemi covid-19 memaksa setiap sekolah mewajibkan guru dan siswanya melakukan pembelajaran secara daring dari rumah. Hal tersebut membuat guru dan siswa dalam waktu yang singkat harus mempersiapkan seluruh vasilitas pendukung pembelajaran. Sedangkan di Kabupaten Malang, para guru fisika masih belum begitu akrab dengan pembelajaran daring, maka pendampingan dan pelatihan pembelajaran daring dengan memanfaatkan moodle sangat dibutuhkan. Kegiatan diawali dengan studi literatur dan lapangan, perencanaan, pemberian materi, demosntrasi dan praktek dan diakhiri dengan kegiatan evaluasi. Untuk mengetahui keberhasilan program, kami menyebarkan kueisioner (n = 13 item) kepada seluruh peserta tentang persepsi terhadap pembelajaran menggunakan moodle dan memantau perkembangan pemahaman guru melalui moodle yang telah dikembangkan. Guru fisika didampingi dan dilatih untuk membuat pembelajaran daring melalui moodle dan variasi model moodle yang sudah pernah diperoleh. Peserta pelatihan dan pendampingan yang diselenggarakan secara daring berjumlah 40 guru fisika di wilayah Kabupaten Malang yang meliputi 34 orang guru fisika SMA dan 6 orang guru fisika MA. Walaupun kehadiran guru tidak bersamaan masuk room meet, tetapi setiap guru selalu masuk setiap hari. Namun, yang aktif mengerjakan pembuatan moodle hanya 25 orang guru yaitu 24 orang guru SMA dan 1 orang guru MA. Peserta yang membuat moodle tersebut bervariasi ada yang hanya membuat Assignment untuk materi dinamika, sampai ada yang lengkap membuat assignment, quiz, dan file untuk materi mekanika, dinamika, usaha dan energi, serta impuls dan momentum. Berdasarkan respon peserta pada angket terkait pelatihan dan pendampingan penyusunan moodle didapatkan 75,19% peserta merespon baik pembelajaran dengan moodle. Kata kunci: pelatihan-pendampingan; moodle; pandemi covid-19; guru fisika.. ABSTRACTThe impact of covid-19 outbreaks forced every school to require teachers and students to do online learning from home. This makes teachers and students in a short time must prepare all the learning support facilities. While in Malang Regency, physics teachers are still not so good with online learning, so online learning assistance and training by utilizing moodle is needed. The programme have began with literature and field research, planning, materials provision, demonstrations, and practices, and concludes with evaluation. To assess the program's performance, we provided a questionnaire (n = 13 questions) to all participants regarding their perceptions of learning with Moodle and simplifying the teacher's knowledge through the produced Moodle. Physics teachers are accompanied and trained to make online learning through moodle and variations of moodle models that have been obtained. The trainees and mentoring held online amounted to 40 physics teachers in malang regency which included 34 high school physics teachers and 6 MA physics teachers. Although the presence of teachers does not coincide with entering the room meet, but every teacher always enters every day. However, who actively do the creation of moodle only 25 teachers, namely 24 high school teachers and 1 MA teacher. Participants who make the moodle vary there are only making Assignments for dynamic materials, until there are complete assignments, quis, and files for mechanical materials, dynamics, work and energy, as well as impulses and momentum. Based on the participants' responses to the questionnaire related to training and mentoring in the preparation of moodle, it was found that 75.19% of participants responded well to learning with moodle. Keywords: training- mentoring; moodle, pandemic covid-19; physics teacher.

Internal and external catalysis in boronic ester networks

In dynamic materials, the reversible condensation between boronic acids and diols provides adaptability, self-healing ability, and responsiveness to small molecules and pH. Recent work has shown that the thermodynamics and kinetics of bond exchange determine the mechanical properties of dynamic polymer networks. However, prior studies have focused on how structural and environmental factors influence boronic acid–diol binding affinity, and design rules for tuning the kinetics of this dynamic bond are lacking. In this work, we investigate the effects of diol (or polyol) structure and salt additives on the rate of bond exchange, binding affinity, and the mechanical properties of the corresponding polymer networks. To better mimic the environment of polymer networks in our small-molecule model systems, we incorporated proximal amide groups, which are used to conjugate diols to polymers, and included salts commonly found in buffers. Using one-dimensional selective exchange spectroscopy (1D EXSY), we find that both proximal amides and buffering anions induce significant rate acceleration consistent with internal and external catalysis, respectively. This rate acceleration is reflected in the stress relaxation of gels formed using PEG modified with different alcohols, and in the presence of salts containing acetate or phosphate. These findings contribute to the fundamental understanding of the boronic ester dynamic bond and offer new molecular strategies to tune the macromolecular properties of dynamic materials.

In-situ-grown silver–polymer framework with coordination complexes for functional artificial tissues

Sensorized actuators are critical to imitate proprio-/exteroception properties of biological neuromuscular systems. Existing add-on approaches, which physically blend heterogeneous sensor/actuator components, fall short of yielding satisfactory solutions, considering their suboptimal interfaces, poor adhesion, and electronic/mechanical property mismatch. Here, we report a single homogeneous material comprising seamless sensing-actuation unification properties at nano-/molecule levels, in which built-in sensing functions originate from the actuator architecture itself. In-situ-grown silver nanoparticles and metal-ligand complexes cooperatively create a silver–polymer framework (SPF) that is stretchable (1200%), conductive (0.076 S/m), and strong (0.76 MPa in-strength). SPF displays concomitant multimodal sensing (mechanical and thermal cues) and sensorized actuation capabilities, which include proprio-deformation and external stimuli perceptions (simultaneous with load-lifting ability up to 3700× of own weight). In view of its human somatosensitive muscular systems imitative functionality, the reported SPFs bode well for use with next generation functional tissues including artificial skins, human-machine interfaces, self-sensing robots, and otherwise dynamic materials.

MATERIAL OPTIMIZATION AND DYNAMIC MATERIALS

The paper is about the connection between material optimization in dynamics and a novel concept of dynamic materials (DM) defined as inseparable union of a framework and the fluxes of mass, momentum, and energy existing in time dependent material formations. An example of a spatial-temporal material geometry is discussed as illustration of a DM capable of accumulating wave energy. Finding the optimal material layouts in dynamics demonstrates conceptual difference from a similar procedure in statics. In the first case, the original constituents are distributed in space-time, whereas in the second - in space alone. The habitual understanding of a material as an isolated framework has come from statics, but a transition to dynamics brings in a new component - the fluxes of mass, momentum, and energy. Based on Noether theorem, these fluxes connect the framework with the environment into inseparable entity termed dynamic material (DM). The key role of DM is that they support controls that may purposefully change the material properties in both space and time, which is the main goal of optimization.

3D processing map and high-temperature deformation behaviour of Fe–0.05C–0.015N–0.13P Steel

Steels alloyed with high phosphorus should be developed for those applications where both strength and corrosion resistance are required. Structural steels such as rebars are manufactured using high-temperature deformation. Hence, thermo-mechanical behaviour of Fe-0.13P-0.05C -0.015N steel is considered using high temperature compression experiments after austenitization at 1050 °C for 10 s. The temperatures selected were between 750 and 1050 °C and at intervals of 50 °C. The rates of strain varied from 0.001 to 10 s−1. Microstructural evolution was studied with the help of optical and scanning electron microscopy. Modified dynamic materials model is used to draw a processing map. The processing map helps in determining the domains which are safe for hot working. This alloy steel can be safely processed in the area confined by the rates of strain between 1 and 10 s−1 as well as the temperature interval of 900 to 1000 °C.

Characterization of Hot Deformation Behavior of Ti-Al-Nb-Zr-Mo-Cr Alloy

The hot deformation behavior of Ti-Al-Nb-Zr-Mo-Cr titanium alloy has been investigated using a Gleeble-1500D thermal simulation test machine in the temperature range of 855°C~1015°C,at constant strain rate from 0.01 s-1 to 10s-1 and with height reduction of 45%. The flow curves characteristic under different deformation parameters show significant difference. According to the stress-strain curves of the alloy and its stress characteristics, the Arrhenius constitutive equation was obtained. The average activation energy is about 541 kJ/mol in the α+β field, and about 243 kJ/mol in the β field, respectively. Based on the dynamic materials model, the processing map is generated, which shows that the peak efficiency domain appears at the temperature of 874°C~900°C and the strain rate of 0.001 s-1~0.06s-1 with a peak efficiency of 0.58 at about 887°C/0.001s-1.

A New Method of Testing the Dynamic Deformation of Metals

This paper presents the characteristics of a modernized rotary hammer equipped with a new measuring system based on strain gauges for recording short-term signals. The stand makes it possible to carry out dynamic tensile and bending tests in the range of linear speed of the exciting element from 5 to 40 m/s. Initial tests of dynamic deformation and structural studies in the form of fractures carried out on a representative group of metallic materials allowed determining the correlation “strain rate–strain structure”. The proposed new methodology of dynamic materials testing is an original achievement of the authors and may be an effective tool for assessing the properties of construction materials under conditions of dynamic deformation. In practice, the test results can be used to design the structures of energy-consuming elements of vehicles and aircraft load-bearing elements subjected to dynamic loads. Having an extensive database of results from dynamic tests will allow verifying the correctness of calculations of the structure with the use of the finite element method.